Generally, a radiation tube accelerates an electron emitted from an electron emitting source at high voltage to irradiate a target with the electron to generate radiation such as an X-ray. The radiation generated at this time is emitted in all directions. PTL 1 discloses a transmission X-ray generation apparatus in which X-ray shielding members are placed on an electron incident side and an X-ray emission side of a target to shield unnecessary X-rays.
In order to generate a radiation suitable for radiation imaging, a high voltage needs to be applied between an electron emitting source and a target to irradiate the target with an electron beam with high energy. However, generally, generation efficiency of radiation is extremely low, and about 99% of consumed power generates heat at the target. Since the generated heat increases the temperature of the target, a unit for preventing heat damage to the target is required. PTL 2 discloses an X-ray generation tube in which a cooling mechanism is provided around an X-ray transmission window to increase heat radiation efficiency of the target.